Digital ink-jet printing technology is a method for directly transmitting, processing and printing data in which steps of plate-making and proofing in a traditional printing process are omitted, and at the same time, as computer technology and control technology are introduced, the printing process is simplified and speeded up and the printed product is flexible. Of various movement ways of an imaging component relative to a printed body, the digital ink-jet printing device referred to herein is a digital ink-jet printing device in which the imaging component is static and the printed body moves relative to the imaging component so as to form an image by ink-jet printing. Due to restrictions of a resolution and a width of the imaging component itself, in this kind of digital ink-jet printing devices, an arrangement of superimposing the imaging components at staggered positions is mostly used to improve the resolution and spliced imaging components are used to widen the printed width. Since the digital ink-jet printing device uses a non-contact printing and it is necessary to control an imaging position of an ink droplet precisely in the printing process, currently the digital ink-jet printing devices are mostly used for full rotary printing devices or sheetfed printing devices, i.e. mostly used for printing devices in which the printed body moves in a single direction, and are less used for printing devices in which movements of the printed body are relatively complex (for example, an intermittent rotary printing device used in a traditional printing process).
FIG. 1 shows a schematic view of an installation mode of imaging components in a digital ink-jet printing device. As shown in FIG. 1, since all imaging components have a certain physical size, in the digital ink-jet printing device in which an expansion is mainly achieved by splicing, adjacent imaging component groups can not be installed in the same straight line, there is a certain physical distance between the imaging component groups.
For example, taking three imaging component groups as an example, assuming the imaging component group 1 and the imaging component group 3 are installed in a straight line, there is a distance a between the imaging component group 2 and the imaging component group 1. If three imaging component groups are controlled to print simultaneously, as shown in FIG. 2, there must be the distance a between printed images of the imaging component groups 1 and 2, thereby the entire image cannot be rendered.
In a full rotary printing device, since the printed body moves in a relatively single way and the printed body always moves forward, the problem may be solved by controlling time of ink-jet printing performed by each of the imaging component groups. In particular, it is assumed that the printed body moves along the following direction: the printed body first passes the imaging component groups 1 and 3, and then passes the imaging component group 2. In this case, the imaging component groups 1 and 3 are controlled to print images simultaneously and the imaging component group 2 is delayed with the distance a, so when images printed by the imaging component groups 1 and 3 reach the imaging component group 2, the imaging component group 2 begins to print. In this way, integrity of the image can be ensured.
As for a printing device in which movements of the printed body are more complex, for example an intermittent rotary printing device, since the printed body of the intermittent rotary printing device moves forward and backward, that is, the printed body doesn't always move forward, there is a backward process. Still taking above three imaging component groups as an example, the printed body moves bi-directionally, it moves forward (i.e. it passes the imaging component groups 1 and 3 and then passes the imaging component group 2), and then it moves backwards (i.e. it passes the imaging component group 2 and then passes the imaging component groups 1 and 3), thus a circle is completed, and so on.
FIG. 3 shows a curve diagram of a speed of the printed body of the intermittent rotary printing device during a forward stage. As shown in FIG. 3, in a printing process, the intermittent rotary printing device accelerates the printed body (A. stage of acceleration) and when the speed of the printed body is accelerated to a predetermined speed, the printed body is in uniform motion for a certain distance (B. stage of uniform motion), and then the intermittent rotary printing device decelerates the printed body (C. stage of deceleration), preparing for a backward movement. Throughout this process, the printed body always moves forward. Assuming a distance that the printed body moves forward during the acceleration process is L1, a distance that the printed body moves forward at the constant speed is L2 (which is referred to as a skip distance) and a distance that the printed body moves forward during the deceleration process is L3, then during the entire forward process, a distance L that the printed body moves forward is L1+L2+L3. However, in practice, the intermittent rotary printing device performs printing only during the constant speed stage, that is, among the forward distances, only the distance L2 is valid and other distances are invalid. Subsequently, the printed body moves backward for a distance L1+L3 during the backward stage in which the printing is not performed.
When the digital ink-jet printing device is used for the intermittent rotary printing device, ink-jet printing is only performed during the constant speed stage in the forward stage in order to match with the printed image. Following above control mode of the full rotary printing device, after entering the constant speed stage, the imaging component groups 1 and 3 perform ink-jet printing, and the imaging component group 2 performs the printing after delaying a distance a. Thus, an image illustrated in FIG. 4 may be obtained. That is, during the constant speed stage, a distance that the printed body moves is L2, a valid ink-jet printing distance of the imaging component groups 1 and 3 is L2, and a valid ink-jet printing distance of the imaging component group 2 is L2−a. In order to ensure integrity of the image, a length of the ink-jet printed image may be selected to be less than L2−a, so during the constant speed stage, the entire image can be ink-jet printed completely. Thus, not only the integrity of the image can be ensured, but also a control mode being the same as that of the full rotary printing device can be used, however, the medium in length of a is wasted during every constant speed stage and the production efficiency is also reduced.